Electromagnetic device



- Aug. 7, 1928. 1,679,765

C. L. FARRAND EI'AL ELECTROMAGNETIC DEVICE Filed Nov. 5, 1926 ATTORN 5Y5.

Patented Aug. 7', 1928.

UNITED STATES "PATENT OFFICE.

CLAIR L. FARBAND, F FOREST HILLS, NEW YORK, AND ERNEST 3088. OF EAST ORANGE, NEW JERSEY; SAID ROSS ASSIGNOR T0 FARRAND MFG. CO. INC., OF LONG ISLAND CITY, NEW YORK, A. CORPORATION OF NEW JERSEY.

ELECTROMAGNETIC DEVICE.

Application filed November 5, 1926. Serial No. 146,351.

This invention relates to electromagnetic devices such for instance as the type used in radio loud speakers for actuating the diaphragm. More particularly the invention relates to an armature assembly adapted for use in such an electromagnetic device.

A well known type of electromagnetic actuating device for radio loud speakers comprises a field magnet having four pole pieces, and an armature each end of which lies between and is acted upon by two of the pole pieces. A fiat spring is disposed at right angles to the armature and is rigidly secured to it. The ends of the spring are anchored to some rigid part of the device in such a way that the spring serves to resiliently hold the armature in a central position between the pole pieces. The spring is usually made of bronze or the like. In radio loud speakers, the direct current which passes through the coils of the electromagnetic actuating device exerts a constant pull on the armature in one direction when the speaker is in use. It has been found in prac tice that in the case of electromagnetic ac tuating devices of the type described above or of any type in which the spring performs a similar function, if the spring is made of bronze or any other material heretofore used the above mentioned constant pull on the armature gradually deforms the spring until the armature at its ends rests against two of the pole pieces. This is due to the fact that bronze and other materials heretofore used for the spring do not have the characteristic of being able to permanently resist the constant pull of the armature in one direction. The spring gradually gives way to the pull of the armature until the ends of the armature abut against the pole pieces as above stated. Of course, this action may be extremely slight as the air gap between the pole pieces and the armature is ordinarily very small and the spring does not have to be deformed or distorted to a great extent in order to allow the armature to come in contact with the pole pieces. lVhen this condition occurs the electromagnetic actuating device is rendered inoperative and it becomes necessary to repair it.

Spring steel has the characteristic of being able to permanently resist a constant force such as that described above but heretofore it has not been practical to employ spring steel for the armature spring because it is customary to braze the spring to the armature and tempered spring steel cannot be brazed Without destroying its temper. I have succeeded in making an eflicient electromagnetic actuating device for radio loud speakers in which the armature is resiliently held in its central position by a tempered steel spring by starting with spring steel in an untempered condition, soldering it to the armature and thereafter tempering the spring steel. I take advantage of the fact that spring steel in an untempered condition can be brazed Without affecting it. This makes it possible to produce an electromagnetic actuating device for loud speakers in which the armature is resiliently held in its central position between the pole pieces and will not eventually move into contact with the pole pieces by reason of any gradual yielding of the spring.

One object of the invention is to provide an electromagnetic device having an improved armature assembly which will be free of the above-mentioned disadvantages of armature assemblies heretofore used.

Another object of the invention is to provide an improved armature assembly for electromagnetic devices and an improved method of making it.

The invention is illustrated in the accompanying drawings in which:

Fig. 1 is a top plan view of an electromagnetic actuating device having an arma ture assembly constructed in accordance with the invent on;

Fig. 2 is a vertical section taken on the line 22 of Fig. 1;

Fig. 3 is a vertical section taken on the line 33 of Fig. 1;

Fig. 4 is a top plan view of the armature assembly;

Fig. 5 is a vertical section taken on the line 55 of Fig. 4; and

Fig. 6 is a vertical section taken on the line 66 of Fig. 5.

The electromagnetic actuating device illustrated in the draw ngs comprises a permanent magnet 1 to which the pole members 2 and 3 are secured. The pole member 2 has a pair of pole pieces 2 and 2" and the pole member 3 has a pair of corresponding pole pieces 3 and 3". An armature 4 is mounted between the pole pieces in such a way that one end of the armature lies between the pole piecesl2 and 3 and the outer end of the armature lies between the pole pieces 2 and 3 as best shown in Fig. 2. The armature 4 is resiliently held in its central position between the pole pieces by means of the flat spring-5 intersecting the armature at right angles thereto and anchored at its ends by means of the screws 6 to an aluminum frame 7 secured to the pole members 2 and 3. In the particular construction shown in the drawings the plane of the spring 5. is at right angles to the plane of the armature 4. The upper end of the. armature 4 has soldered to it a. rod or wire 8 which if desired can be connected directly with the diaphragm of the radio loud speaker. However, in order that the plane of the electromagnet 1 may be parallel with the plane of the diaphragm, the vibrations of the rod 8 are preferably transmitted to a second rod 9 through the lever systcm 101112. The second rod 9 being arranged at right angles to the plane of the electromagnet, it is possible to position the electromagnet in a plane substantially par allel with the plane of the diaphragm. The lever system 101112 may comprise a channel-shaped member of sheet metal anchored at its ends to the aluminum frame 7 as shown at 13 and 14 and weakened and bent at two points such as 15 and 16 in such a way that these weakened portions act as hinges. In this way the portion of the channel-shaped member from the point 13 to the weakened portion 15 forms one lever 10, the part between the weakened portions 15 and 16 constitutes a second lever 11 and the part between the weakened portion 16 and the point 14 constitutes a third lever 12. In this way vibrations imparted to the lever 10 are transmitted through the lever 11 to the lever 12. The latter in vibrating about the point 14 as a fulcrum causes the rod 9 to vibrate longitudinally. The rod 9 is secured directly to the lever 12 at about the mid point of the latter. It will be understood that the lever 10 can flex slightly where it is anchored at 13 and likewise the lever 12 can flex slightly where it is anchored at 14.

It is the armature assembly including the spring 5, the armature 4 and the rod 8 with which this invention particularly deals and these parts will now be described more in detail and the method of making them will also be described.

Figs. 4, 5 and 6 show the armature assembly separated from the other parts of the electromagnetic device. The spring 5 of the armature assembly is made of spring steel and is provided with a pair of openlugs 17 and 18 to receive the screws 6. It

is also provided with a slot 19 extending part way across the width of the spring. The armature 4 is made of iron and is provided on opposite faces with slots 20 and 21 so that the armature may be moved transversely into engagement with the spring and so that the slots 20 and 21 will engage the edge portions of the spring at the slot, all in such a way that these two members will intersect and be interlocked one with the other. ture 4 at their junction as represented at 22 and the rod 8 is soldered to the upper end of the armature 4 as represented at 23.

In making the ari'i'iature assembly the armature and spring are first interlocked in the manner above described it being understood that the spring steel used for the part 5 is in an untempered condition at the beginning of the process. The two parts are then brazed together at 22. The spring steel may be brazed to the armature without attecting the spring steel because the steel is still in an unten'iperet'l condition. The parts 6 brazed together are then subjected to the necessary temperature to temper the spring steel. This may be accomplished by passing it through an electric furnace which will heat the spring steel to a temperature of approximately 1300 F. WVhen the devices are being made on a commercial scale the armatures with the attached springs may be passed in succession through the electric turnace on a conveyor. It is not known definitely whether or not the solder melts during this heating, but this is immaterial because even if the solder melts it again hardens when the armature assembly is discharged from the electric furnace and as the parts are mechanically interlocked during the heating operation they do not come apart nor change their relation. When the tem perature has been raised to approximately 1300 F. the armature assemblyis suddenly cooled as by immersing it in oil and this tempers the spring steel. In the commercial operation of the process the armature assemblies may be discharged directly from the electric furnace into an oil bath.

The armature assemblies are then sub- JGCtGCl to a temperature of approximately 450 F. for an interval of time to draw the temper and in the commercial operation of the process this step may be carried out in an electric furnace similar to the first one in which the temperature is maintained at the proper point and through which the armature assemblies may be passed in succession on a suitable conveyor. The armature assemblies should be subjected to the heat of the second electric furnace for about fifteen seconds in order to properly draw the temper. The rod 8 is then soldered to the armature 4 and this may be readily done as the armature is made of iron. If desired,

'75 The spring 5 is soldered to the arma not] the rod 8 may be soldered to the armature before the assembly is passed through the second electric furnace.

The particular relation shown in the drawing between the armature and the spring has been adopted to adapt the armature assembly to the particular type of electromagnetic device shown in the drawing. It will be understood, however, that the relation between these parts will depend upon the type of electromagnetic device in which the armature assembly is used. A particular type of electromagnetic actuating device has been shown in the drawings merely for the purpose of illustrating one application of the invention.

I claim:

1. An armature assembly for electromag netic devices comprising an armature and a strip of spring steel disposed in a plane at right angles to the plane of the armature, said strip of spring steel having a slot extending part way across the same and the armature having grooves on opposite faces to receive the edge portions of the steel strip at the slot, the steel strip and armature being brazed together at the junction between the two.

2. The method of making an armature assembly for electromagnetic devices which comprises brazing a strip of untempered spring steel to an armature and thereafter tempering the strip of spring steel.

3. The method of making an armature assembly for electromagnetic devices which comprises brazing a strip of untempered spring steel to an armature and thereafter tempering the strip of spring steel and then drawing the temper at a predetermined temperature.

4. The method of making an armature assembly for electromagnetic devices which comprises brazing a strip of untempered spring steel to an armature, thereafter heating the spring steel and immersing it in a cooling liquid to temper it and then maintaining the spring steel at a predetermined temperature for a period of time to draw the temper.

5. The method of making an armature assembly for electromagnetic devices which comprises brazing a strip of untempered spring steel to an armature, thereafter heating the spring steel to about 1300 F. and immersing it in a cooling liquid to temper. it, and then maintaining the spring steel at a temperature of approximately 450 F. for a period of time to draw the temper.

6. The method of making an armature assembly for electromagnetic devices which comprises mechanically attaching an untempered strip of spring steel to an armature, brazing the strip of spring steel to the armature1 and thereafter tempering the spring stee 7. The method of making an armature assembly for electromagnetic devices which comprises brazing a strip of untempered spring steel to an iron armature, thereafter tempering the spring steel and then soldering a rod to the iron armature.

In testimony whereof we affix our signatur'es.

CLAIR L. FARRAND ERNEST ROSS. 

